Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Research Article Fair Adaptive Bandwidth and Subchannel Allocation in the WiMAX Uplink | Hindawi Publishing Corporation EURASIP Journal on Wireless Communications and Networking Volume 2009 Article ID 918261 13 pages doi 2009 918261 Research Article Fair Adaptive Bandwidth and Subchannel Allocation in the WiMAX Uplink Antoni Morell Gonzalo Seco-Granados and Jose Lopez Vicario Telecommunications and System Engineering Department TES Autonomous University of Barcelona UAB 08193 Bellaterra Spain Correspondence should be addressed to Antoni Morell Received 2 July 2008 Revised 22 November 2008 Accepted 29 December 2008 Recommended by Ekram Hossain In some modern communication systems as it is the case of WiMAX it has been decided to implement Demand Assignment Multiple Access DAMA solutions. End-users request transmission opportunities before accessing the system which provides an efficient way to share system resources. In this paper we briefly review the PHY and MAC layers of an OFDMA-based WiMAX system and we propose to use a Network Utility Maximization NUM framework to formulate the DAMA strategy foreseen in the uplink of IEEE . Utility functions are chosen to achieve fair solutions attaining different degrees of fairness and to further support the QoS requirements of the services in the system. Moreover since the standard allocates resources in a terminal basis but each terminal may support several services we develop a new decomposition technique the coupled-decompositions method that obtains the optimal service flow allocation with a small number of iterations the improvement is significant when compared to other known solutions . Furthermore since the PHY layer in mobile WiMAX has the means to adapt the transport capacities of the links between the Base Station BS and the Subscriber Stations SSs the proposed PHY-MAC cross-layer design uses this extra degree of freedom in order to enhance the network utility. Copyright 2009 Antoni Morell et al. This is an open access article distributed under the Creative Commons
